[AI Evaluation] Microsoft.Extensions.AI.Evaluation evaluators don't handle responses that used tool calls well.

### Description

As an example, the `CoherenceEvaluator`, makes use of the `TryGetUserRequest()` extensions method which doesn't "try" very hard as it only looks at the last message to see if it's `Role` is `ChatRole.User`, and if it's not it returns `false` and sets the `userRequest` object to `null`. When tools are available to the model and are used, the last message in the conversation will likely be a tool message with a `Role` of `ChatRole.Tool`.

I think the Evaluators should be looking back to the last message that has `Role` set to `ChatRole.User`, or at least as far back the previous message with `ChatRole.Assistant` and the evaluation prompt should be updated to take the tool messages into account as well, as the Coherence of the response may depend on what data they return as well.

### Reproduction Steps

1. Have a `IChatClient` instance
2. Call `.GetResponseAsync(chatMessages, callOptions, cancellationToken)` with a `callOptions` object that has tools configured and a `chatMessage` with content that would cause the model to use at least one of the configured tools.
3. Create a `CoherenceEvaluator` instance and call `.EvaluateAsync` passing in the messages from the response.

### Expected behavior

The evaluator is able to judge the coherence of the response, and include the most recent user request and any tools message since in it's reasoning.

### Actual behavior

The evaluation include a thought chain including something like:

> First, I need to identify what the QUERY is - but I notice the QUERY field is completely empty. There is no question or prompt provided

### Regression?

_No response_

### Known Workarounds

_No response_

### Configuration

.NET 9
Microsoft.Extensions.AI, Microsoft.Extensions.AI.Evaluation and Microsoft.Extensions.AI.Evaluation.Quality version 9.9.0

### Other information

https://github.com/dotnet/extensions/blob/53ef1158f9f42632e111d6873a8cd72b803b4ae6/src/Libraries/Microsoft.Extensions.AI.Evaluation.Quality/CoherenceEvaluator.cs#L89-L91

https://github.com/dotnet/extensions/blob/53ef1158f9f42632e111d6873a8cd72b803b4ae6/src/Libraries/Microsoft.Extensions.AI.Evaluation/ChatMessageExtensions.cs#L17-L44

https://github.com/dotnet/extensions/blob/53ef1158f9f42632e111d6873a8cd72b803b4ae6/src/Libraries/Microsoft.Extensions.AI.Evaluation.Quality/CoherenceEvaluator.cs#L182-L184